See also:

Temperatures at Aklavik
 
Mean Summer Temperatures

Arctic Borderlands Ecological Knowledge Co-op

What is happening?

• Each summer the upper layer of soil in permafrost areas thaws and then freezes again in the winter. This graph shows the average depth of thaw, measured at the end of summer, at a series of 12 sites at Illisarvik on the northern end of Richards Island, NWT.
• The depth of summer thawing varies from year to year and 1998 stands out as a summer with the greatest amount of thawing. The spring and summer of that year were unusually warm (following an El Nino winter)
• There is a trend towards a greater depth of thaw between 1983 and 2008 so that the ground thaws about 6 cm deeper by the end of this 25 year period.

Why is it happening?

• Ground temperatures depend on both air temperatures and the ability of heat to penetrate into the soil. A thick layer of ground vegetation, especially moss, will limit the amount of heat the soil can absorb during the summer, while deeper snow cover in winter may slow the rate of cooling as the ground refreezes.

Why is it important?

• Increases in air temperatures expected with global climate change are likely to result in increases of the depth of thaw. The increased depth at which thaw occurs can have many effects at the ground surface. The melting of ground ice, where permafrost is ice-rich, can cause ground slumping and increases in soil moisture, which in turn may affect surface erosion, and the stability of man made structures such as buildings and roads.
• As thaw depths increase plants may benefit as their roots can access soil nutrients which were previously frozen and unavailable.

Technical Notes

• These data were taken from Figure 12 in C.R. Burn and S.V. Kokelj 2009. The environment and permafrost of the Mackenzie Delta area. Permafrost and Periglacial Processes 20: 83-105.